Even low levels of radiation are already affecting bird populations near the Fukushima Daiichi nuclear disaster, according to a new study in Environmental Pollution. Surveying birds in Fukushima Prefecture, an international team of scientists showed that higher levels of radiation correlated with smaller populations. The scientists attribute this to the fact that the power plant’s malfunction occurred in March, early in the breeding season.

“The data presented here constitute the first investigation of initial biological community responses to the radioactive fallout from the Fukushima disaster,” the authors wrote.

The team also compared the effects of radiation on bird populations at Fukushima to birds near Chernobyl. All 14 species that inhabit the two locations appeared to be more affected by increasing radiation in Fukushima than they were at Chernobyl. At Fukushima, increasing radiation correlated with greater bird population decreases. However, a general drop bird abundance was more strongly associated with increasing radiation dose in Chernobyl, most likely because many species in the worst contaminated areas are long gone.

“The prolonged, relatively larger impacts on Chernobyl communities point to possible sustained, longer term impacts on organisms that may reflect cumulative, multigenerational consequences of mutation accumulation within populations,” the authors wrote. “The disaster at Chernobyl, and now Fukushima, provide unique opportunities to assess the risks and hazards of prolonged exposure to mutagenic contaminants that likely have relevance for other communities inhabiting the regions affected by these disasters.”